The overall aim of our program is to explore and explain the differences that appear in the surfaces of cells following tumorigenic "transformation". We are interested in all the aspects of research in this area, but over the next few years will concentrate much of our attention on describing and explaining what happens to the surface of secondary chick embryo fibroblasts following transformation by Rous sarcoma virus. This system has already received detailed biological analysis. In addition, we are attracted by the availability of excellent temperature sensitive mutants and are actively engaged in studies with TS68, a mutant isolated by Hanafusa and coworkers. The specific problems we will be investigating in the near future are the decreases in specific plasma membrane proteins following transformation, cell surface proteolysis, and the control of transglycosylase mechanisms in normal and transformed cells.